The new feature is an enhancement to Firefox’s Private Browsing mode, which deleted users’ browsing history and cookies after they closed a private window. Tracking Protection adds an extra layer of privacy to that by blocking code embedded in websites that tracks the way people behave around the Web. That means it will block a lot of ads, along with analytics tools and some social sharing buttons in order to help users keep their browsing habits more closely under wraps.

It solves one of the key problems with the private browsing modes that browsers like Firefox, Chrome and others have pushed in the past: while they may keep a user's browsing history under wraps for people looking at that person's computer, tracking features of websites will still be able to keep tabs on them.

The change isn’t good news for companies that rely on tracker-based advertising to make money, however. Although Firefox users are only a small (and shrinking) part of total browser users — and Private Browsing users a smaller percentage of that still — the new feature means that they won’t get money from ads that aren’t displayed to people using Tracking Protection.

That said, advertisements that don’t track users will still show up when users have Tracking Protection enabled, so that’s one way for publishers to continue monetizing their work.

It’s all part of a push Mozilla is making (through Firefox) to provide tools for users who want to curb tracking of their browsing habits, but the company says that it’s not out to kill advertising or ad-based businesses on the Web. Denelle Dixon-Thayer, the company’s Chief Legal and Business Officer, said in a recent blog post that the organization wants to push an open ecosystem that gives publishers and developers a way to monetize their work while balancing user privacy.

All of that is not to say that people who use tracking protection will be able to keep their browsing completely private. Internet service providers and network administrators will still be able to see what they do, for example.

Mozilla is also in a unique position to roll the new feature out. Both Microsoft and Google have advertising-based businesses that rely on tracking users in order to make money, so it’s not in their best interests to build similar features.

Were Apple to launch a similar feature in its Safari browser, it would likely provoke a swift, negative reaction from publishers that the company is trying to court to build apps for its platform and share content through iOS 9’s News app.

Features like this may drive renewed interest in Firefox at a time when the browser is losing market share to Google Chrome. Creating these sort of user-centric features will be key to differentiating Mozilla’s offering in a crowded and tough market, especially when the company’s competitors may not be as interested in building similar functionality.

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